Shelves hold shortcuts or icons to the more common tools that you might use in maya. There is a shelf for each defined work area such as polygon modeling, surface modeling, animation, dynamics, rendering and a few more depending on which version of the software you are using. This video tutorial show you how to use shelves, load custom icons and shortcuts, and use the shelf editor to manipulate shortcut positions, and remove them from the shelf in question.

Launch Video (5m 20s)

Tutorial Overview

The shelf is a panel that stores common tools within maya, so you don't have to constantly change modes to access the menu structure holding the tool you need. Click on the different tabs, to access the shelf you are after.

* image: the polygons shelf

The shelf editor will help you edit icon labels, tooltips and even the icon image.
If you shelves are missing, or you have turned them off to maximise the work area, you can turn it back on by heading up to Display > UI Elements > Shelf

* image: the shelf editor